Conventionally, there have been known semiconductor light emitting devices (hereinafter referred to as wavelength-converted RGB solid light sources) configured to emit at least light components of the three primary colors, red (R), green (G) and blue (B), with the combined use of solid light emitting elements (e.g., light emitting diodes, hereinafter referred to as LEDs) and phosphors that absorb primary light emitted by the solid light emitting elements and convert the primary light into light with a longer wavelength.
Examples of conventionally-known combination structures of the wavelength-converted RGB solid light sources are as follows.    (1) A combination structure including an ultraviolet LED and red, green and blue phosphors (see Patent document 1, for example)    (2) A combination structure including a blue LED and green and red phosphors (see Patent document 2, for example)    (3) A combination structure including an ultraviolet LED, a blue LED, and red and green phosphors (see Patent document 10, for example)    (4) A combination structure including a blue LED, a green phosphor and a red LED (see Patent document 3, for example)    (5) A combination structure including a blue LED, a green (lime green) phosphor, a green LED and a red phosphor (see Patent document 4, for example)    (6) A combination structure including a blue LED, a green LED and a red phosphor (see Patent document 5, for example)    (7) A combination structure including an ultraviolet LED, blue and green phosphors and a red LED (see Patent document 6, for example)
In addition to the combination structures described above, there also has been invented a combination structure including an LED having light emitting layers that emit two kinds of light with different wavelengths, and phosphors, for example (see Patent document 7, for example).
These conventional semiconductor light emitting devices are created primarily as illumination light sources, and from most of them, each wavelength component is outputted in a state of being adjusted so that light with an arbitrary color temperature or light with a light bulb color, for example, can be emitted (see Patent documents 5 and 8, for example).
Applications of the wavelength-converted RGB solid light sources to backlights for display devices (e.g., backlights for liquid crystal displays) also have been pursued. For example, applications of a combination structure of an ultraviolet LED and red, green and blue phosphors, a combination structure of a blue LED and green and red phosphors, and a combination structure of an ultraviolet/violet LED, a blue LED, and green and red phosphors, etc. have been studied, and liquid crystal displays, etc. using such backlight sources also have been proposed (see Patent documents 9 and 10, for example).
In a wavelength-converted RGB solid light source having the above-described combination structure including an ultraviolet/violet LED, a blue LED, and green and red phosphors, the green phosphor that emits green light and the red phosphor that emits red light both have broadband light absorption properties. This light source is created to solve the problem of an absorption loss of blue light, which occurs due to the blue light not being absorbed entirely but only partially, and high output is achieved particularly by the excitation of a green phosphor activated with Eu2+ or a red phosphor activated with Eu2+ having an excitation peak in a near-violet-violet wavelength range of 300 to less than 420 nm with excitation light in the region of the excitation peak.
Accordingly, this light source is based on the premise that a phosphor made of SrAl2O4:Eu2+, Eu2+-based thiogallate (e.g., SrGa2S4:Eu2+) or the like, for example, having an absorption spectrum shifted toward a blue wavelength range and also having broadband light absorption properties in a near-ultraviolet-blue wavelength range [e.g., a phosphor activated with Eu2+ that emits green light on the basis of a (4f)7-(4f)65d1 electronic energy transition of Eu2+] is used as the green phosphor, not a green phosphor that substantially does not absorb blue light [e.g., a phosphor that emits green light on the basis of a (3d)5-(3d)5 electronic energy transition of Mn2+].
Furthermore, a structure in which the above-described green phosphor does not cover a light extraction surface of the blue LED is considered to be a preferred form, and specifically, a structure in which the green phosphor and the red phosphor are at least separated spatially from the blue LED has been proposed.
It should be noted that a highly-precise measurement technique for absolute external quantum efficiency and absolute internal quantum efficiency of phosphors, which will be mentioned in this specification, already has been established and the efficiencies can be evaluated with the use of phosphor samples (see Non-patent document 1, for example).